To meet the communication needs of mobile users, various public radio networks, such as a digital mobile communication system GSM (Global System for Mobile Communication), have been developed. Besides public networks with a wide coverage area, various wireless local area networks and private networks have also been developed, such as professional mobile radio or private mobile radio (PMR) systems. They are dedicated radio systems developed primarily for professional and governmental users, such as the police, military forces, oil plants, different types of company networks etc. One example of digital PMR systems is TETRA (Terrestrial Trunked Radio) which is defined by ETSI (European Telecommunications Standards Institute).
At the very beginning, GSM specifications defined a short message service which has become one of the most used supplementary services offered by the GSM. Now a wide variety of services, such as news, weather, jokes, etc. are accessible via short messages. In addition to text-only short messages, services comprising multimedia messages are also provided today. These various message services have in common that they are typically asynchronous transfer of data, transferred on system control channels between actual signalling. In other words, they use the same basic principles as the short message service of the GSM.
Since the short message service has been so popular in the GSM, corresponding messaging services are also included in other systems. For example, TETRA standards define an SDS (short data service) whose basic principles are similar to the messaging services based on the short message service of the GSM.
However, the definitions of different standards for the same type of messaging service differ from each other. Therefore, a subscriber of one system cannot send a messaging service message to a subscriber of another system. For example, TETRA subscribers cannot send text-only SDS messages to GSM subscribers, and GSM subscribers cannot send short messages to TETRA subscribers.
One solution to the above problem is to define an interface between the messaging services of these two different systems. However, since there are also other systems and systems are evolving rapidly, one interface definition is not enough, but several different interfaces have to be defined, which makes the systems more complicated and more difficult to maintain.